As is known, the use of construction elements made of expanded plastics, preferably expanded polystyrene, in the forms of boards or section members of suitable shape and size serving thermal and sound insulation functions, has long been accepted by the building industry.
It is also known that, in order to confer adequate self-supporting properties to such construction elements, one or more reinforcing section bars of a suitable shape must be incorporated into the mass of expanded plastics.
Thus, for example, European Patent EP 0 459 924 discloses a self-supporting construction element made of expanded plastics material, specifically a floor element, which comprises a substantially parallelepipedic central body in which a reinforcing section bar, made of a thin metal sheet shaped as an I-beam, is integrated during the molding step.
While construction elements of this kind have on the one hand a light weight, a comparative ease of installation and a low cost, on the other hand their application in the art and flexibility of use have been restrained heretofore by their poor fire-resisting properties.
This inadequate resistance to fire is essentially related to the fact that construction elements made of expanded plastics show an insufficient capability to securely hold outer covering layers, such as the plaster layers used for the outer surface finish.
When exposed to fire, in fact, the expanded plastics soon shrinks into a shapeless mass of reduced volume, with the ensuing separation of the outer covering layers and rapid collapse of the whole structure.
In addition, an undesirable separation of the outer covering layers may be caused in some instances by a premature "aging" of the plastics surface to which these coverings adhere, a separation which may be further fostered by exposure to heat sources, dusts, fumes, vapors, or chemical substances coming from a source close to the construction elements.